Pattern coater



July 16, 1968 I WARNER 3,392,702

PATTERN COATER Filed Aug. 5, 1964 {a F1 6. 6 824 5 22 4M United States Patent 3,392,702 PATTERN COATER Edgar Warner, RR. 1, Box 91, Middletown, Ohio 45042 Filed Aug. 5, 1964, Ser. No. 387,630 8 Claims. (Cl. 118-246) ABSTRACT OF THE DISCLOSURE The invention involves the application of either low or high solids mineral pigment coatings in slurry form to moving paper webs to form a coated surface thereon, by applying the coating by means of an applicator roll moving at a different peripheral speed than that of the linear speed of the web, the coating having been formed in a regular acute angled helix on the applicator roll by transfer thereto from a rubber blanketed transfer roll running in contact with a small diameter metering and pattern forming roll which limits and at the same time forms the pattern of coating to be transferred to the applicator roll. The helical pattern is generally formed at an angle of 30 to 60 with respect to the line of movement of the web hence the invention relates also to apparatus for performing the stated method.

This invention is concerned with an apparatus for and method of coating a substrate of indefinite length. More particularly, the invention is concerned with the application of and apparatus for applying controlled amounts of a solid containing coating to a substrate to form a web having a surface characterized by smoothness, levelness, uniformity of coating and freedom from hole-s, skips and the like. Since these latter characteristics are of prime concern in the production of high quality printing papers, the present method and apparatus will be described in connection with the application of paper coatings wherein a cellulosic web of indefinite length is coated with an ink receptive coating defined generally as an aqueous dispersion of one or more mineral pigments and an adhesive binder. Without delving in detail into specific coating ingredients, but for illustrative purposes, such a coating might'consist of calcium carbonate and/r clay as the pigment constituent, and casein as the adhesive constituent, both dispersed in water which serves as an aqueous carrier. Various anti-foaming agents, dyes and other additives may be included in the coating material. Too, the solids content of the coating may vary depending on a number of variables all of which is well known in the art.

The mere application of mineral pigment coating to paper is not new, nor is it new to provide an apparatus for applying such coatings. Examples of some forms of these devices are amply illustrated in the prior art as refiected in Warner Patents 2,970,564 and 3,084,663, among others concerned with this art. In each case the considerations involved are always those previously mentioned, i.e. to secure adequate coverage of the web; to obtain a uniform distribution of the coating on the web; to form a level coated surface free of ripples or stipples; and to assure the deposit of adequate coating to cover the web so that the print receptively of the surface is uniform.

This present invention, then, is concerned with an apparatus and method to accomplish the desired results and to enable accurate control over the application of coating to the web.

An object of the invention therefore, is to produce a coating apparatus for coating Webs of indefinite length.

Another object of the invention is to produce a coating apparatus for use in applying high solids coatings.

3,392,702 Patented July 16, 1968 An additional object of the invention is to provide a coating apparatus capable of producing high quality printing paper.

Still another object of the invention is to produce a coating apparatus which will enable a uniform, level coated surface to be attained.

Another object of the invention is to provide a coating apparatus which will deposit a metered regulated amount of coating to the substrate.

Still a further object of the invention is to provide a novel coating method.

An additional object of the invention is to provide a method of coating which results in uniform application of the coating material to the substrate.

An object of the invention is also to provide a novel method of applying aqueous dispersions of a mineral pigment and adhesive to a paper substrate.

A further object of the invention is to provide a method of coating paper which results in a uniformly high quality, coated surface which may itself form the printing surface or which may serve as a foundation or precoat for a subsequently applied coating as, for example, during a cast coating or trailing blade" top coat operation.

These and other objects of the invention which may not have been specifically set forth, but which are, nonethe-less inherent therein, are accomplished by a method of coating which comprises the steps of providing a source of coating, transferring coating from said source to a web, said transfer including the steps of forming the coating into a regular pattern, moving said pattern to a point adjacent the web and then applying said coating to the web by wiping same thereon to form a controlled amount of uniformly applied coating to the surface of said web.

The stated objects and method may be accomplished by means of a coating apparatus including a coating source, and means for transferring coating from said source to said web, said means comprising a pattern forming roll, means in contact with said pattern forming roll and acting therewith to provide controlled amounts of coating on said pattern forming roll, a transfer roll receiving the formed coating from the pattern forming roll and in contact with a web, said transfer roll turning with the web :but at a speed differential .with respect thereto so as to wipe the coating onto the surface of the web to smooth out the pattern into a level uniform coating on said surface. Further said apparatus may comprise means for heating or cooling said transfer roll as may be expeditious to accomplish the desired results.

Having described the invention in its broad aspects, consideration will now be given to the details thereof, reference being made to the drawing attached to and forming a part of the description and wherein FIG. 1 is a side elevational view in somewhat schematic form illustrating one form of the invention,

FIG. 2 is a top plan view of the device shown in FIG. 1,

FIG. 3 is an enlarged view of a portion of the pattern forming means used in FIGS. 1 and 2,

FIG. 4 is a view showing a further modificationof the invention,

FIG. 5 is an illustration showing the relationship of the pattern forming means with respect to movement of the web, and, finally,

FIG. 6 is a schematic elevational view showing at least one installation of the apparatus in an on machine coating arrangement.

Turning initially to FIGURES 1 and 2, it will be seen that one form of the apparatus may comprise a coating pan 1 which may be filled with a coating material C.

Usually such coating is recirculated within pan 1. Mounted on suitable journals 14 and extending within pan 1 and rotatable generally in a clockwise direction is a coating pickup roll 3. This roll is partially immersed within the coating C and preferably provided with a rubber covering 5. It has been found that a suitable covering of a P and J hardness of 150 is adequate for most purposes, though the covering may be modified to suit a given condition.

In contact with the pickup roll 3 and journalled for rotation in any conventional mounting in a counterclockwise direction is a pattern roll 7. This roll which is, in the combination, essential to the invention, may comprise a small diameter pipe having a helically grooved outer circumferential surface. The grooved surface is comprised of multiple threads dis-posed at a helix angle of approximately the range of to degrees which has been found eminently satisfactory in the application of most coating materials. Preferably, the threads are of such a cross sectional configuration that no sharp edges are present at the circumference of the roll which cut the rubber surface of the coating pickup roll 3. A suitable thread configuration is shown in the enlarged view of FIG. 3, illustrating a portion of the pattern forming roll and wherein the threads comprise V-shaped grooves 9 and wherein the intersection of the converging walls 11 of adjacent grooves 9 defining the tops of the threads at 13, are blunted or flattened to remove sharp edges. It is believed obvious, too, that a rolled thread, i.e. a thread in the form of helical corrugations having a generally semi-circular cross sectional configuration at the top and bottom would serve the purpose equally well.

The pattern forming roll 7 is journalled in suitable frame members, not shown, as is strictly conventional and is driven, as is pickup roll 3 by any conventional drive arrangement 10, gears, chain and sprocket, belt, etc., which will impart to the rolls the proper rotative direction and speed, the latter of which will be discussed later herein.

In order, however, to prevent fiexure of the pattern roll, it is desirable to support same at suitable points throughout its length, i.e. width across the web. This may be simply accomplished by the utilization of a series of hard rubber pads or rollers 15 equally spaced across the machine and carried by suitable brackets 17 in turn bolted, riveted or otherwise suitably fixed to coating pan 1. Thus, the contact pressure between the pickup roll 3 and the pattern roll 7 is uniform throughout the length, i.e. width, of the two rolls from end to end.

Disposed above and also in contact with the pickup roll 3, is the transfer roll 19 of smaller diameter than the pickup roll but usually of larger diameter than the pattern roll 7. The transfer roll is provided with a very fine, smooth chrome plated circumferential surface. This roll also driven by any suitable drive means is rotated in a clockwise direction and at a peripheral speed which is equal to between /2 and /s of the speed of the web W with which it is in edge-to-edge contact. Again, the roll 19 is conventionally supported and journalled in a coater frame of usual design and any conventional, but variable speed, drive means may be employed to rotate same in the direction of speed of the web but at an angular velocity which will cause the above stated relationship between peripheral roll speed and linear web speed.

As seen in FIG. 1, the web W, moving from left to right, is drawn over the transfer roll 19 so that the web is bent into an obtuse angle between its entry and exit sides as it passes thereover. While this angle is not critical in the sense that a specific value can be stated for the angular relationship, it has been found that, for any given set of conditions, too great an angle or wrap over roll 19 results in the formation of a ripple pattern in the surface, while too little wrap will result in the formation of a stipple pattern in the coated surface. Since factors such as coating weight, web speed, transfer roll speed,

web weight, etc., all are factors involved in what degree of wrap is desirable, it suffices to say that the degree of wra-p of the web W over roll 19 is greater than a line contact. For the purpose of controlling the wrap of the web on roll 19, a pair of vertically adjustable fly rolls 21 and 23 are positioned above the web and to either side of transfer roll 19.

Turning now to FIG. 3 in some detail, a further coater, referred to hereafter as a pool or pond coating arrangement is disclosed. In this instance a coating pan and pickup roll are dispensed with entirely. Instead a pattern roll 25 is paired with a rubber covered transfer roll 27 of equal diameter. Coating is deposited in the nip formed between these two rolls from a suitable nozzle 29 forming a pond or pool P at this nip.

Roll 27 is similar to the previously described transfer roll 3 having a rubber covering of the same characteristics.

Roll 25, which is the pattern forming roll is provided with a surface having helical grooves or threads therein of the same general configuration and at generally the same helix angle as previously described.

Disposed above the rubber covered roll 27 and in contact therewith and with web W is an applicator roll 31, chrome surfaced and generally identical with the applicator roll of FIG. 1.

It will be noted from the arrows, that the rolls 25 and 27 turn in opposite directions, i.e. toward each other so that the rotation of the applicator roll 31 is in the direction of web travel. Also with the rolls 27, 25 rotating toward each other the coating pool P can be maintained while a certain amount of coating will be carried through the nip and metered onto the transfer roll 27 in the desired helical pattern by roll 25. Subsequently, this coating is transferred onto the applicator roll 31 and thence wiped onto web W.

The particular coated arrangement shown in FIG. 4 and described in detail immediately above has particular application where the coating must be applied to the Web in substantial weight because of the characteristics of the web. In such cases it is desirable to formulate and apply the coating with a high solids content, i.e. solids to liquids ratio. This type of coating operation often precedes a further coating application and hence the apparatus may sometimes be referred to as a precoater or base coater. As distinguished from the arrangement of FIG. 4, the arrangement of FIG. 1 is generally utilized for the application of coatings of lower solids content.

In FIG. 6 there is disclosed at least one coating arrangement wherein a coating apparatus of the type shown in FIG. 1 is utilized in a paper machine. In such an arrangement the coating apparatus may be positioned between dryer roll sections 40 and 50. Depending on the position of the coating apparatus, i.e. its vertical position with respect to the dryer roll 51, the use of fly roll 23 may or may not be necessary. In any event, the web W passes from dryer section 40 through the coating apparatus and thence into dryer section 50. It should be understood, however, that use of the invention is not limited to on machine coating operations but is equally adaptable to off machine use. Similarly, the form that the invention may take pan or pool type of arrangement is not to be construed as limiting either arrangement to one or the other uses.

Considering again FIG. 2 it will be seen that advantageously both the pattern forming roll 7 and transfer roll 19 are disclosed as being hollow. Suitably affixed to both rolls, as by slip ring or any other type of suitable connection are conduits 55 and 56 respectively and on the other ends conduits 57 and 58 respectively. Thus, it is possible to admit a heat transfer medium, either heating or cooling, to these two rolls 7 and 19. Generally it will be found desirable to heat the transfer roll 19 and to cool the pattern forming roll 7. The cooling of roll 7 particularly, when applying aqueous dispersions of mineral pigment coatings since cooling helps to prevent sticking and accumulation of the coating in the helical valleys of threads 9. Further, heating of transfer roll 19 has the affect of making the coating, which it carries onto web W, more fluid and hence the wiping action of the roll 19 against the web is considerably more effective in smoothing or flowing out the coating on the web surface.

From the above description of the apparatus, it will become obvious that various modifications and changes therein will occur to those skilled in the art, which modifications and changes will be feasible therein to carry out the novel method of coating which comprises the application of coating by the steps of forming coating received from a source, either pan 1 or nozzle 29 into a regular ribbed pattern roll 7 or roll 25, thereafter transferring the pattern of coating to a point adjacent the web, i.e. at the nip formed between the rolls 27 and 31 or rolls 3 and 7 and thereafter applying the coating to the web by wip ing action, with a difference in web speed over either transfer roll 31 or roll 19 acting to meter and smooth the coating so applied.

Having thus described the novel method and several forms of apparatus for carrying out the invention, it should be apparent that the spirit and scope thereof is limited only as defined hereafter, where what is claimed is:

1. A coating apparatus comprised of a source of pigmented coating, means for transferring said coating from said source to a moving coating receptive web, said last mentioned means including a pattern carrying roll in contact with said coating source; means defining a pattern forming roll in contact with said pattern carrying roll and defining a nip therewith to provide a controlled amount of coating in a ribbed pattern on said pattern carrying roll, said pattern forming roll being characterized by a surface comprised of a regular series of outwardly opening divergent walled valleys and interdigitated ribs therebetween; a smooth surfaced transfer roll in contact with said pattern carrying roll and the moving web; means for rotat ing said rolls, said means rotating said pattern carrying and said transfer rolls in the same direction and further rotating said transfer roll in the direction of movement of the web being coated and at a peripheral speed less than the web speed to transfer coating from said pattern carrying roll onto the web by wiping action thereagainst.

2. A coating apparatus as defined in claim 1 wherein said pattern forming roll includes a threaded exterior surface, the threads being disposed at an angle of from 30 to with respect to the direction of web travel.

3. A coating apparatus as defined in claim 2 wherein the threads are helical in form.

4. A coating apparatus as defined in claim 1 wherein means for transferring coating from said source of coating to said pattern forming roll comprises a pan and said pattern carrying roll is positioned so that its lowermost point is immersed in said pan, said last-mentioned roll being in contact with said pattern forming roll.

5. A coating apparatus as defined in claim 3 wherein said means for transferring coating from said source to said pattern forming roll comprises a roll in contact with said pattern carrying roll and defining a nip therewith, and further includes means for depositing coating in said nip.

6. An apparatus as defined in claim 1 wherein said pattern carrying roll is provided with a resilient surface characterized by a P and J hardness of about 150.

7. An apparatus as defined in claim 1 wherein said transfer roll rotates at a speed of from /s to /2 of web speed.

8. An apparatus as defined in claim 1 wherein said web contacts said transfer roll over an area greater than a line contact area.

References Cited UNITED STATES PATENTS 2,605,684 8/1952 Nagels et al. 1,851,761 3/1932 Everett. 2,199,228 4/1940 Obenshain et a1 117-111 2,560,572 7/1951 Haywood et a1 117-111 2,772,184 11/1956 Wolfe et al 117-64 3,054,716 9/1962 Bergstein et a1. 117-111 X ALFRED L. LEAVITT, Primary Examiner.

E. B. LIPSCOMB, III, A. M. GRIMALDI,

Assistant Examiners. 

